The invention refers to a method and kit for detecting human or animal blood.
The use of chemiluminescent reactions for the detection of blood traces is known from the prior art.
The term “chemiluminescence” means the emission of light that follows a chemical reaction. Among the most commonly used reagents for detecting traces of blood there is the organic molecule 5-amino-2,3-dihydro-1,4-phthalazinedione, commercially known as luminol, the oxidation of which produces chemiluminescence. This reaction is catalytically promoted by transition metal ions, including the iron ions in blood haemoglobin. Such a reaction is widely used in forensic applications, particularly for detecting the so-called latent blood traces, namely extremely low quantities of blood that are not detectable through direct observation, which may persist on various types of surfaces even after washings and/or partial removal or degradation by natural agents, detergents or agents of different nature.
In forensic applications, luminol is generally used in aqueous formulations, which comprise, besides luminol, an oxidizing agent and an alkaline agent.
The classical luminol formulations for forensic applications are the Weber/Wilson formulation, which consists of luminol, sodium or potassium hydroxide and hydrogen peroxide (K. Weber, Dtsch Z. Gesamte Gerichtl. Med. 57 (1966) 410-423) and the Grodsky formulation, consisting of a mixture of luminol, sodium carbonate and sodium perborate in distilled water (M. Grodsky, et al., J. Crimin. Law Criminol. Police Sci. 42 (1961) 95-104).
The International patent application PCT/FR2003/001299 describes a further luminol formulation, marketed with the trade name Bluestar®, comprising a luminol compound, an oxidizing agent and a base, both preferably diluted in an aqueous solvent, wherein the luminol compound is present in an amount providing a concentration from 1 to 20 mM in the final composition, the anti-oxidizing agent is hydrogen peroxide that is present in an amount providing a concentration from 25 to 100 mM in the final composition, and the base is NaOH that is present in an amount providing a concentration from 25 to 500 mM in the final composition. According to what is described in PCT/FR2003/001299, the composition allows to instantly detect extremely low amounts of blood not only under totally dark conditions but also under reduced light conditions.
Even if the luminol method is well established and widely used in forensic applications both in the United States of America and in many European countries and the use thereof has been introduced in Italy during the last decade, its performance is limited by the overall short duration of the chemiluminescent phenomenon that generally runs out within about 30 seconds (Barni, Filippo et al., Talanta 72 (2007) 869-913). The possibility of acquiring a correct photographic documentation of the chemiluminescent phenomenon, which is of considerable and increasing importance during the preliminary and procedural phases, is thus thwarted.
In order to overcome the drawbacks of the prior art, the present invention provides a method of detecting human or animal blood on a surface, comprising the step of applying to the surface to be investigated a liquid luminol composition comprising a luminol compound, hydrogen peroxide or other peroxidic oxidising agent and an alkaline agent in an amount providing a pH within the range of 10 to 14, characterised in that, prior to said liquid luminol composition, a suspension of inorganic powder selected from the group consisting of silicas, aluminas, titanias, alkaline metal oxides, alkaline earth metal oxides, zinc oxides, zirconias, water insoluble phosphates, micro- and nano-particles of oxide or non oxide semiconductors, functionalised derivatives thereof and mixtures containing varying proportions thereof is applied onto the surface to be investigated, wherein the inorganic powder or the functionalised derivative or the mixture are suspended in an aqueous solvent or in an organic solvent.